Which answer accurately describes the difference between speed and velocity? question 8 options:
a. speed can be constant or it can change. velocity is always constant.
b. speed requires direction. direction doesn't matter when calculating velocity.
c. speed is the distance per unit of time. velocity is the displacement per unit of time.
d. speed is the same as average velocity. velocity is used to calculate acceleration.

Imagine that someone pushes one marble toward a motionless marble. would there still be action-reaction forces involved in the collision? how might the marbles’ motions be changed? ?

Glass has a hardness that is in the middle of the hardness scale. what is the hardness of glass?

Aplayground slide is 8.80 ft long and makes an angle of 25.0° with the horizontal. a 63.0-kg child, initially at the top, slides all the way down to the bottom of the slide. (a) choosing the bottom of the slide as the reference configuration, what is the system's potential energy when the child is at the top and at the bottom of the slide? what is the change in potential energy as the child slides from the top to the bottom of the slide? (include the sign of the value in your answer.)